I am using the Hello World program which something like 8-bit Counter.http://www.arduino.cc/en/Tutorial/ShiftOut

The problem is, I found that the LED stop at the middle (ie. restart when counter to ~37)However, when I add Serial.beign(9600) and start serial monitor the output at the same time.The counter seems work normally....

http://www.youtube.com/watch?v=Oa0Uo376EUM

I had tested various sample codes and still find the same problem, did I miss something important ?